- Force of interest ($\delta$) measures interest instantaneously, conceptually derived by allowing the compounding frequency ($m$) to approach infinity. This is equivalent to continuous compounding
- Relationship to Effective Rate: $1+i = e^{\delta}$
- Time-Varying Force of Interest $\delta_t = \frac{a'(t)}{a(t)}$
- Shouldn’t be too common as compound interest has a constant force of interest
- Accumulation Function: $a(t) = \exp\left(\int_0^t \delta_\tau \, \mathrm{d}\tau\right)$